The Internet provides access to a wide variety of content. Publishers of webpages and other types of first-party content often monetize their content by allowing sponsored third-party content (e.g., advertisements) to be integrated therewith. A programmatic Internet advertising system can be used to automate the selection and integration of third-party content with the first-party content. Third-party content providers typically create content items for presentation on a client device. It can be difficult and challenging for third-party content providers to create effective and attractive content items.